1. Field of the Invention
The present invention relates to a touch pad, and in particular to a touch pad having reduced number of circuit boards and cost and having an increased yield of products.
2. Description of Prior Art
Existing touch pads are primarily divided into four categories including resistance-type, capacitance-type, acoustic-type and optical-type based on their principles of sensing signals. The capacitance-type touch pad is dust-proof, fire-resistant and high-definition, so that it is widely used. The capacitance-type touch pad is configured to identify the position of contact based on a change of capacitance. More specifically, the capacitance-type touch pad is configured to identity the coordinates of a contact point based on a change of capacitance between electrodes caused by the approach of an object (such as a finger or other conductor).
The capacitance-type touch pad currently available in the market is made of two circuit boards and has a four-layer structure. As shown in FIG. 1, the touch pad is constituted of a first circuit board 1 and a second circuit board 2. Each of the first circuit board 1 and the second circuit board 2 has an upper surface and a lower surface respectively. The upper surface of the first circuit board 1 is etched to form columns of first conductors 11. The first conductors 11 penetrate one side of the first circuit board 1 to form a column of connecting terminals 111 on the lower surface of the first circuit board 1. Furthermore, the lower surface of the first circuit board 1 is etched to form rows of second conductors 12. The second conductors 12 form a row of connecting terminals 121 on one side of the lower surface of the first circuit board 1.
The lower surface of the second circuit board 2 is provided with a control chip 3. The lower surface of the second circuit board 2 is etched to form columns of leads 21 and rows of leads 22 connected to the control chip 3. One ends of the columns of leads 21 and the rows of leads 22 penetrate the second circuit board 2 respectively and form columns of connecting lines 23 and rows of connecting lines 24 on the upper surface of the second circuit board 2. The columns of connecting lines 23 and the rows of connecting lines 24 are electrically connected to the columns of connecting ends 111 and the rows of connecting ends 121 respectively.
Although the four-layer structure formed by the first circuit board 1 and the second circuit board 2 can achieve a crisscross arrangement of the first conductors 11 and the second conductors 12, the total thickness of the first circuit board 1 and the second circuit board 2 inevitably increases the thickness of a touch pad formed by these two circuit boards. As a result, such a four-layer touch pad cannot satisfy the requirements for compact design of modern portable electronic devices. On the other hand, the change of capacitance detected by the two separated layers of first conductors 11 and the second conductors 12 may be different, which causes erroneous determination of signals. In order to compensate for this error, the cost of providing circuits for signal analysis and the period of operation will be inevitably increased.
On the other hand, during the manufacture of the above-mentioned four-layer touch pad, four surfaces of the two circuit boards are coated with copper clad and then subjected to an etching process with optical masks. As a result, a large portion of the copper clad will be etched, which causes the waste of material and adverse effects to the environment.
According to the above, the prior art has disadvantages as follows:
(1) the thickness of the four-layer touch pad restricts the compact design of an associated electronic product;
(2) since at least two circuit boards are used, the materials and at least two manufacturing processes are needed, which causes the increase in total cost; and
(3) a complicated process for signal analysis and a long period of operation are needed.
Therefore, it is an important issue for the present inventor and the manufacturers in this filed to solve the above-mentioned problems in prior art.